Can I only Render light that psses through an object?
See this .blend file. I used nodes with the Transmission Depth node and two emission shaders joined with a mix shader. Set the green one to 0 strength and it should have the desired effect. I'll post a screen shot of the node set up in a moment. (The node set up for the lamp. It's a point source directly above the glass sphere.)

Here is the node set up.

The green is what will go away. The pink it what will be rendered.

Green disabled (strength is set to 0).